The stationary valve plate in slide gate valves of this type is axially clamped near its outer periphery (U.S. Pat. No. 3,955,591). To create the necessary displacement path for the movable valve plate, the housing has an inner chamber which is increased in diameter opposite the adjacent pipelines. To obtain a perfect seal between the valve housing and the adjacent pipelines, even when the valve is incorrectly installed, a certain size of sealing surface between the valve housing and the pipeline is specified, so that the sealing surface extends radially inwards over the supporting area of the stationary valve plate, the supporting area being predetermined by the size of the inner chamber of the housing. The supporting area, facing towards the inner chamber of the housing, of the stationary valve plate is consequently smaller than the supporting area between the stationary valve plate and the end of the adjacent pipeline. This causes the stationary valve plate to become distorted when the bolts connecting the housing to the flanges of the pipeline are overtightened and especially if they are tightened non-uniformly. This leads to a nonuniform seating of the displaceable valve plate against the stationary valve plate, so that a perfect sealing function of these two valve plates is no longer ensured. This can also be caused when there is a high medium pressure.